1. Field of the Invention
The present invention relates to chemical-amplification-type negative resist compositions. More particularly, it relates to a chemical-amplification-type negative resist composition which exhibits high sensitivity, high definition and excellent thermostability, can be patterned into films of various thicknesses, and achieves a resist pattern having an excellent profile. Additionally, it relates to a method for forming a negative resist pattern using the chemical-amplification-type negative resist composition.
2. Description of the Related Art
Recently, since electronic parts such as semiconductor devices and liquid-crystal display devices are progressively finely manufactured, higher sensitivity and definition are required of resists used for manufacturing such parts, and resist patterns should be formed so as to have more excellent profiles. Concerning resists satisfying such requirements, attention is paid to chemical-amplification-type resists whose solubilities in developer solutions vary according to a catalytic action by an acid generated by the irradiation of radiant rays, and a large number of chemical-amplification-type negative resist compositions have been proposed.
In the manufacture of electronic parts using such a chemical-amplification-type negative resist composition, photolithography is employed, in which the chemical-amplification-type negative resist composition is applied onto a substrate such as a silicon wafer, the resultant is then subjected to irradiation through a mask pattern and developed to form a resist pattern, and etching is performed using the resist pattern as a protective film. As to the radiant rays used in photolithography, increasingly preferred are shorter wavelength rays such as ultraviolet rays, deep UV, and excimer laser beams derived from KrF, ArF or the like. Further, the use of an electron beam or a X ray has been considered as a practical option.
For achieving satisfactory sensitivity to such shorter wavelength radiant rays and for obtaining a satisfactory resist pattern, each ingredient in the chemical-amplification-type negative resist composition should be less absorptive for the radial rays. In this view, conventionally used novolak resins cannot be used as resin ingredients of such compositions due to their high absorptivities at such wavelengths, and polyvinylphenol-based polymers have been used since they are less absorptive at such wavelengths. Actually, chemical-amplification-type negative resist compositions containing such polyvinylphenol-based polymers as resin ingredients have been disclosed in, for example, Japanese Patent Laid-Open Nos. 1-293339, 2-15270, 4-163552, 6-67433 and 7-311463. The compositions are, however, inferior in definition.
Aiming to improve definition, Japanese Patent Laid-Open No. 7-238196 discloses a chemical-amplification-type negative resist composition containing an alkali-soluble resin, 4-hydroxystyrene-styrene copolymer, whose styrene content is 5 to 20 mole % and whose weight average molecular weight is 6,000 to 25,000.
The uses of the chemical-amplification-type negative resist composition disclosed in that publication, however, results in a resist pattern inferior in contrast. Further, in any chemical-amplification-type negative resist composition, when the thickness of the resist film is 2.0 .mu.m or more, and particularly 3.0 .mu.m or more, the obtained resist patterns may be mutually crosslinked, namely, a so-called micro-bridging phenomenon may occur, or the top surfaces of the resist patterns may readily become round. In particular, since a thickness of 2.0 .mu.m, and more preferably 3.0 .mu.m, is required of a photoresist film for ion plantation, there is a strong demand for a resist composition capable of achieving high definition even when a thicker resist film should be formed.